A direct link exists between respiratory infections – such as influenza, bronchitis or pneumonia – and heart attack or stroke, according to study results released Thursday in Britain.

In the week following a respiratory infection, the risk from heart attack or stroke can double, researchers said. The connection was discovered after investigators analyzed a database containing medical information for more than 2 million patients. The findings only add to growing calls for heart patients to make sure they get the flu vaccine, experts said.

The link is found only when serious respiratory infections are involved, explained epidemiology professor Tom Meade of the London School of Hygiene.

“A head cold or runny nose doesn’t seem to be a problem,” he noted.